(1) Field of the Invention:
The present invention relates generally to an underwater vehicle launch test facility and, more particularly, to such a facility which permits the vehicle to move laterally and rotate in reaction to hydrodynamic forces acting on it during testing so that realistic vehicle launch dynamics and interactions between the vehicle and the launch facility may be obtained.
(2) Description of the Prior Art:
A number of vehicles are launched from underway submarine vessels ranging from torpedoes and missiles that are several feet in diameter and over twenty (20) feet long to small devices that long. These vehicles are launched from inside tubes having a slightly larger inside diameter than the diameter of the vehicle to be launched. The vehicles are launched into the flow stream created by the vessel's forward motion through the water. Launch is effected by various including means pumping water into the back of the tube which imparts longitudinal motion to the vehicle and carries it outside of the submarine vessel's hull.
The flow stream imports various hydrodynamic forces to the vehicle which tends to divert its longitudinal motion and causes the vehicle to bear against the walls of the launch tube and later deflects its trajectory from its original path once it has left the tube. This may result in vehicle damage, unacceptable vehicle dynamics, or restrictions on the vessel speed and maneuvers prior to and during the launch of the vehicle.
In order to predict how vehicles of various size will react during actual launch from a submarine vessel, it has been suggested to evaluate a vehicle's launch characteristics prior to it's actual use. For example, U.S. Pat. No. 3,314,285 discloses a test facility for evaluating the launch and limited free flight characteristics of a vehicle into a still fluid. This test facility includes releasable brackets that grab and hold the vehicle in an essentially horizontal position prior to launch. At launch initiation, the brackets release their grip on the vehicle and a piston imparts downward motion to the vehicle. Once the vehicle has traveled a certain distance, the vehicle's motion is restrained by cables that attach to the vehicle and the capturing the vehicle in a cubical box whose walls are made of flexible cord in order to minimize damage to the vehicle.
The above-referenced patent discloses basically a drop launch test facility which only provides information on the vehicle itself without taking into account the substantial interactions between the vehicle and the vehicle's launch tube. As a result, the use of this type of facility is no longer favored. It had been found that more realistic results may be obtained by conducting performance tests of a vehicle as the vehicle is being launched from a submarine launcher test facility which simulates actual launch of the vehicle from the launch tube in order to determine the launch dynamics of the vehicle and the interactions between the launch facility-and the vehicle throughout the launch.
Two types of tests are presently used to evaluate vehicle and launcher performance. Both tests utilize a circulating water channel which provides a flow stream operable to generate hydrodynamic forces which will interact with the vehicle during launch. In the first test, after the vehicle is launched it is completely free of the launcher and is allowed to react to the flow stream. This test is referred to as a "free launch test". In the second test, the vehicle is constrained at launch by a rod rigidly affixed to the vehicle's tail. The rod limits vehicle motion to a strictly longitudinal path and the vehicle is prevented from undergoing normal rotational and lateral motions in reaction to the hydrodynamic forces created by the flow stream. This test is referred to as a "captive launch test".
The major disadvantage of the free launch test is that after each launch the vehicle must be manually retrieved from within the water channel and reloaded into the launch tube for the next test. This can take considerable time due to limited accessibility and restrict the number of tests conducted. During free launch testing, the vehicle must also be caught by a net or other mechanism located within the water channel to prevent the vehicle from being damaged by striking the walls of the channel. In addition, tests on certain vehicles may not be permitted in a given water channel due to the risk of damaging the channel if the vehicle is not caught and is carried by the flow stream into the water channel pumps or flow stream conditioning devices.
The major disadvantage of the captive launch test is that it unrealistically restricts the vehicle's motion. Although the captive launch test does provide a benefit in that this test eliminates the need for a net or other mechanism positioned in the water channel, the rigid connection between the rod and the vehicle results in errors in the hydrodynamic forces experienced by the captive vehicle.
Consequently, a need exists for an underwater vehicle test facility which retains some of the benefits of the captive launch test facility and also permits the vehicle to move laterally and rotate in reaction to hydrodynamic forces acting on it during launch to allow realistic vehicle launch dynamics and interactions between the vehicle and the launcher to be obtained.